Energy-saving is the main feature of heat pumps.

Energy-saving is the main feature of air to water heat pumps.

 Heat pumps use electricity to exact heat from the free air or the underground, and transfer the extracted heat into the hot water. A heat pump with 4.0 COP means that the heat pump use 1kw electricity can extract 4kw heat from the free air. So, by calculating the electricity consumption and the electricity price, you can work out the rough cost in one year and compare it with the boiler cost.